The invention relates to an arrangement for measuring a rate of rotation using a vibration sensor, the vibration of which perpendicular to a first axis is excited and measured with the aid of capacitive drive elements, and the rotation of which in a second axis, which is excited by rotation in a third axis under the action of the Coriolis force, is measured with the aid of capacitive measuring elements, the capacitive elements each being formed by fixed electrodes and by electrodes which can be moved with the vibration sensor, and the movable electrodes being jointly connected to a fixed connection.
Rate of rotation sensors are used, for example, in safety systems for motor vehicles. A vibration sensor in the form of a gyroscope has been disclosed, for example, in U.S. Pat. No. 5,955,668. In this case, the rotational vibration is excited with the aid of electrostatic drives. The output signal and a signal for regulating the drives are likewise obtained electrostatically, namely by means of capacitance measurements with the aid of supplied AC voltages. In this case, the amplitude of the AC voltage supplied to the drive is considerably greater than that of the signals obtained from the change in capacitance, with the result that, in particular, the output signal to be processed further in order to determine the rate of rotation is subject to considerable interference. This impairs the measurement accuracy.
The object of the present invention is to specify an arrangement for measuring a rate of rotation, the accuracy of which satisfies high demands and which has a large dynamic range, that is to say very low rates of rotation are also intended to be measured with sufficient accuracy, while no overdriving occurs at high rates of rotation.
In the case of the arrangement according to the invention, this object is achieved by virtue of the fact that the fixed electrodes of the capacitive drive elements can be supplied with excitation voltages, the frequency of which corresponds to the resonant frequency or to a subharmonic of the resonant frequency of the vibration sensor, that capacitive elements which are used to measure the excited vibration can be supplied with an AC voltage at a first measuring frequency which is higher than the frequency of the excitation voltages, and that the fixed electrodes of the capacitive measuring elements are supplied with AC voltages at a second measuring frequency which differs from the first measuring frequency and is higher than the frequency of the excitation voltages.
The arrangement according to the invention can be designed in such a manner that further capacitive measuring elements are provided for the purpose of measuring the excited vibration or the capacitive drive elements are used to measure the excited vibration.
In the arrangement according to the invention, one advantageous and interference-proof possible way of obtaining the output signal which describes the rate of rotation is to use means which, in order to form a signal which represents the rate of rotation, synchronously demodulate a signal tapped off from the fixed connection using the AC voltage at the second measuring frequency and then using the excitation voltage,
Another refinement of the invention provides means which also demodulate the signal tapped off from the fixed connection using the first measuring frequency and use the demodulated signal to regulate the excitation voltages.
The invention makes it possible to operate the arrangement with considerable AC voltages for driving and to accept in the process that the signals which are taken from the second capacitive elements for the purpose of regulating the drive and the signals which are taken from the third capacitive elements for the purpose of forming the rate of rotation signal are also extremely small. However, on account of the small interference components caused by the drive currents, these signals can be evaluated in an effective manner, in particular when using technologies available in the prior art, for example low-noise amplifiers. In this case, in particular, a charge amplifier whose output is connected to a bandpass filter is connected to the fixed connection. As a result, even small remnants of the drive currents are attenuated further.
In order to keep the drive currents occurring at the fixed connection low from the outset, another development involves providing at least four groups of capacitive drive elements, antiphase AC voltage components and the same bias voltages respectively being applied to two of said groups.
This may be carried out, for example, as follows:
U1=U10+U11 sin ωt
U2=U10−U11 sin ωt
U3=−U1
U4=−U2
As a result, the charge currents at the fixed connection are compensated for, whereas the drive torques generated are intensified since the drive torques are proportional to U2. These measures can also be used successfully without the measures in the preceding claims and considerably reduce the interference caused by the excitation voltages.
A person skilled in the art can select, in detail, the frequencies or the ratios of the frequencies to one another taking into account the respectively present circumstances. However, it has proved to be favorable if the first and second measuring frequencies are within a range of 10 times to 500 times the frequency of the excitation voltage.
The invention is suitable for different types of vibration sensors but the vibration sensor is preferably a vibrational gyroscope. However, linearly oscillating vibration sensors, for example, may also be configured according to the invention.
The invention allows numerous embodiments. One of said embodiments is schematically illustrated in the drawing using a plurality of figures and is described below. In the drawing:
The vibrational gyroscope illustrated in
A plurality of arms 5 to 10 having capacitive elements 11 to 16 are situated on the circumference of the ring 3. In the schematic illustration according to
The fixed electrodes 18, 18′ are applied, such that they are insulated, to a substrate which is not illustrated and integrally also has the parts 1 to 17. Methods for patterning the substrate are known in the art and do not need to be discussed in any more detail in connection with the invention.
The electrodes 18, 181 of the capacitive elements 11 to 14 are supplied with AC voltages at the same frequency but with a different phase angle for the purpose of exciting the rotational vibration—the excitation voltage below. In this case, as illustrated in the small diagrams, a DC voltage is respectively superposed on the excitation voltages, with the result that the electrodes 18 and the electrodes 18′ have the same DC voltage components and antiphase AC voltage components. This is effected in order to generate a periodic total torque since the torque generated at the electrode 18, for example, is proportional to the square of the voltage applied there and is thus always positive. Only the sum of the two torques which are generated by the electrodes 18 and 18′ contains the desired AC component.
In order to generate a sufficiently high drive force, the electrodes 17 are interleaved with the electrodes 18, 18′ in a comb-like manner, in which case only two individual electrodes are respectively illustrated for the sake of clarity but the number is considerably higher in practice.
A frequency-controlled oscillator (VCO) 19 having two antiphase outputs 20, 21 is used to generate antiphase excitation voltages which, provided with corresponding bias voltages, are supplied to the capacitive elements 11 to 13. The connection 2 which is explained in more detail below in connection with the operation of obtaining the rate of rotation signal is used to feed back (not illustrated) the currents generated by the excitation voltages. The capacitive measuring elements 15, 16 are used to regulate the rotational vibration, AC voltages which are generated in an oscillator 22 and are at a first measuring frequency f1 being applied to said measuring elements. As likewise explained below, the operation of supplying these AC voltages is used to measure the capacitance of the capacitive elements 15, 16 and thus to obtain a signal which represents the rotational vibration.
The signal at the connection 23 has the spectrum indicated in
In the block diagram according to
Two multipliers 31, 32 in which synchronous demodulation using the measuring frequencies f1 and f2 is carried out are connected to the output A of the filter 30. The demodulated signals are denoted using B and C. Following low-pass filtering at 33, a signal which represents the rotational oscillation of the vibrational gyroscope is present at 34. This signal is supplied to a further multiplier 35 which forms a control loop together with a regulator 36 with the characteristic F(p) and the oscillator 19. As a results both the frequency and the phase angle of the output voltage of the oscillator 19 are controlled in such a manner that a stable oscillation is produced. In order to control the amplitude of the oscillation, the signal at 34 is compared with a reference voltage Uref via an adder 37 and is supplied to a control input of the oscillator 19 via a further regulator 38 with the characteristic G(p), the excitation voltage provided with a DC voltage component being present at the outputs 20, 21 of said oscillator.
In order to generate the rate of rotation signal, the output signal C from the multiplier 32 is passed to a low-pass filter 39. From there, the signal passes to a further multiplier 40 which is also supplied with a signal at the frequency fres, as a result of which said multiplier operates as a synchronous demodulator. The demodulated signal D represents the rate of rotation signal which is passed to an output 42 via an amplifier 41.
Number | Date | Country | Kind |
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10-2006-046-772.8 | Sep 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP07/59607 | 9/13/2007 | WO | 00 | 4/23/2009 |